Anaerobic carotenoid biosynthesis in Rhodobacter sphaeroides 2.4.1: H2O is a source of oxygen for the 1-methoxy group of spheroidene but not for the 2-oxo group of spheroidenone

Abstract Anaerobic biosynthesis of carotenoids in the purple facultative photosynthetic bacterium Rhodobacter sphaeroides was studied using mass spectrometry. We have demonstrated that 18 O from H 2 18 O was incorporated into the 1-methoxy group of spheroidene and spheroidenone, the two major carotenoids produced by this bacterium during photosynthetic growth. Neither water nor CO 2 was shown to provide an oxygen atom for the 2-oxo group of spheroidenone in R. sphaeroides 2.4.1 grown photosynthetically in the absence of molecular oxygen. Possible mechanisms for the anaerobic biosynthesis of spheroidenone in R. sphaeroides are discussed. © 1997 Federation of European Biochemical Societies.